This thesis investigates the potential of coffee-based granulate for Large Scale Additive Manufacturing (LSAM) in sustainable outdoor furniture design. The research is a collaboration between Coffee Based and 10XL, supported by Het Ooievaarsfonds. The project aims to determine whether materials from Coffee Based, made from spent coffee grounds (SCG), can be used to create large-scale 3D-printed furniture, and how their material behavior influences design and manufacturing decisions.

The research attempts to fill a clear gap in the literature. While SCG-based composites have been used in small-scale filament printing, their performance in Fused Granulate Fabrication (FGF) using LSAM has not yet been studied. The project uses a research-through-design approach and follows a double diamond process with the following clear parts: literature review and problem definition, material and printer exploration, design development, and final design and validation.

Three SCG-based compounds provided by Coffee Based were tested: SCG with recycled polypropylene (rPP), bio-based high-density polyethylene (bioHDPE), and thermoplastic starch (TPS). Their sustainable properties are different: rPP contributes to technical circularity through recycling within the technical cycle, bioHDPE is bio-based and derived from renewable feedstock, and TPS is bio-based, biodegradable, and compostable within the biological cycle. The material exploration phase is mainly focused on improving print quality rather than the mechanical properties of the compounds themselves.

Many print tests were performed at 10XL, mostly on a smaller extruder, and in the end, once on the large extruder. The main test variables were flow/extrusion rate, temperature, bed adhesion, print speed, and minimum layer time. Print quality was mainly focused on shape fidelity (overhang, bridging, radii, corner angles, and shrinkage), extrusion consistency, and surface finish. Performance was measured both qualitatively and quantitatively.

Shrinkage turned out to be a major challenge in this research. The TPS compound showed the lowest and most consistent shrinkage (below 0.5%) and had proper adhesion to the print bed without needing additional fixation. In contrast, the rPP and bioHDPE compound showed significant shrinkage levels, and therefore also needed additional fixation to the print bed. While adding chalk to these compounds reduced shrinkage, because it was manually mixed, it led to inhomogeneity and inconsistencies in print quality. Using the TPS compound, successful overhang angles reached up to 40 degrees, while bridging was mainly unsuccessful, due to the continuous flow nature of LSAM. Corner angles smaller than 40 degrees turned out to be unreliable. However, small radii were printable and reliable.

These findings led to the design of an XL 3D-printed prototype that combines the potential of the coffee-based material with the preferences of the stakeholders, within the found constraints of the printing technology.

Overall, this research shows that the provided granulates by Coffee Based have the potential to be used in LSAM with FGF, provided that further development is performed to minimize shrinkage and improve extrusion consistency on the large extruder. Design choices also have to align with material properties and printer possibilities.
Thus, while much is still unknown and challenges towards print quality remain, the project lays the groundwork for further development on using circular, biobased (or waste-based) materials in LSAM.